For uplinks of LTE-Advanced (hereinafter referred to as “LTE-A”) which is an evolved version of 3GPP LTE (3rd Generation Partnership Project Long-term Evolution, hereinafter referred to as “LTE”), introduction of a band extension technique called “Carrier Aggregation (CA)” is under study. CA in LTE-A seeks to realize high speed transmission using a plurality of bundled component carriers (CCs). One component carrier has a bandwidth of maximum 20 MHz.
In LTE-A, it is agreed that a terminal should report PHR (Power Headroom=information on a reserve capacity of transmission power of the terminal) to a base station for each CC. PHR is used by a base station to perform link adaptation (adaptive modulation, channel coding, closed loop transmission power control or the like) of a transmission channel of a terminal. Following equation 1 is a definition equation of PHR used in LTE.
[1]PHR=Pcmax−{10 log10(Mpusch)+Po_pusch+α·PL+Δtf+f(i)}  (Equation 1)
Here, Pcmax is maximum transmission power [dBm] of the terminal, Mpusch is transmission bandwidth [RB] of PUSCH, Po_pusch is a value [dBm] preset by the base station, PL is a path-loss level [dB] measured by the mobile station, α is a weighting factor representing a compensation proportion of path loss and is a preset value, Δtf is an MCS-dependent offset of data transmitted, f(i) is a transmission power control value (e.g., relative value such as +3 dB or −1 dB) in subframe #i and is an accumulation past transmission power control values.
Po_pusch, α and Δtf are parameters instructed from the base station to the mobile station and are values that can be comprehended by the base station. However, PL and f(i) cannot be exactly comprehended by the base station. That is, f(i) is a parameter instructed from the base station to the mobile station but the mobile station may not be able to receive the instruction (that is, the mobile station may not be able to detect a control channel (PDCCH)). Since the base station cannot decide whether the mobile station has successfully received the instruction or not, if the mobile station fails even once to receive the transmission power control value of the base station, there will be a mismatch in recognition between the mobile station and the base station. Thus, since the base station cannot exactly comprehend PHR of the mobile station, the base station needs to have PHR reported from the mobile station.
Furthermore, PHR of LTE is reported from the terminal to the base station under predetermined conditions determined beforehand by the base station (e.g., in a predetermined cycle or when PL varies more than a threshold). To be more specific, PHR of LTE is reported on PUSCH as MAC (Medium Access Control) information, of transmission data PHR of LTE is reported as information of 6 bits.
Parameters (Po_pusch, α) of equation 1 and scheduling information (Mpusch, Δtf, f(i)) are set independently among CCs. Thus, PHR for each CC is calculated using parameters and scheduling information of each CC according to equation 1.
Furthermore, as a method of reporting PHR when a plurality of UL CCs are set for a terminal, it is agreed that the terminal feeds back PHRs of all set (configured) CCs to the base station using a UL channel when triggered for PHR reporting. However, even when a plurality of UL CCs are configured for the terminal, UL CCs actually, used at certain timing may be some of the plurality of configured UL CCs. In this case, the base station does not report any UL grant (transmission format information; UL transmission bandwidth, MCS information or the like) to the terminal through unused UL CCs. Therefore, for UL CCs with no UL grant allocated, the terminal cannot calculate transmission power and PHR of PUSCH (see FIG. 1). In FIG. 1, rectangles denote regions (that is, PUSCH regions) to transmit PUSCH signals. Rectangles enclosed by dotted lines in particular denote PUSCH regions with no UL grant allocated (not transmitted) and rectangles enclosed by solid lines denote PUSCH regions with UL grants allocated (transmitted).
Here, at PHR report timing, Mpusch and Δtf in equation 1 are not configured for the terminal in CCs with no UL grant allocated in the PUSCH region. For this reason, the terminal cannot calculate PHR using equation 1 in a conventional manner. Thus, it is necessary to define a calculation equation (called “Reference Format” or “Virtual Format”) to calculate PHRs of CCs with no UL grant allocated.
For PUCCH, the following items are agreed. That is, when no PUCCH is transmitted, it is agreed that all terminals use bandwidth=1 RB, Δf (offset dependent on PUCCH format)=0 dB in the reference format of PUCCH used to calculate PHR of PUCCH (that is, reserve capacity of transmission power of the terminal in PUCCH transmission) (Non-Patent Literature 1).